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RE: [FlyRotary] Returnless Fuel System - Fuel Cooler
Hi Leon;
I'm a little late responding as I spent the
weekend rebuilding my dirt bike with one of them ole fashioned piston engines
what go up & down to make something go round 'n round? What a goofy
idea!
Anyways, back to the subject at hand. Pressure
recovery ?... so what? Well without pressure differential there is no flow.
None. I realize that jets are used to meter flow and that a restriction is an
impediment to flow, however my point was that if the EFI pump has an outlet of
say 1/8" into a 3/8" line (or in Bob's case, his 1/4" return line) it does not
have the equivalent flow of a 1/8" line. While it will not have full flow
of an unrestricted line due to permanent pressure loss, it will recover much of
its pressure resulting in a much greater flow than would be provided by a
1/8" tube. To calculate this the Beta ratio of the "orifice" is required,
however it really isn't that important. Besides, I can't find right now the
required formula. I should get back to studying this as I return to school for
4th year in 2 months and I can be assured that there will be at least one
twisted question concerning this on the incoming exam.
Someone had mentioned drilling out the pump
outlet to reduce this restriction, but that would be a really bad idea. The pump
outlet is usually sized smaller than the pipe that it is sized for in order to
provide adequate back pressure to the pump to prevent cavitation. If you drill
out this outlet, then bubbles can/will form in the impellor and the resulting
cavitation will result in less flow and quite possibly the vapour lock that we
are trying to avoid. This restriction does not diminish the requirement for a
proper sized tube to be plumbed to it in order to achieve rated
flow.
Just my 2 bits worth
Cheers
Todd
So I just can't see what the size of an
attached pipe has to do with the flow rate through a "vena contracta"
("vena constricta"??). You also say "but much of this pressure is
recovered downstream" Hmmmmmm, ... I say "so what"??. We aren't
interested in pressure drops or pressure recovery, ... it's flow rates
that are the SOLE issue, and the capacity of an open flow 1/4
inch line to get rid of the fuel dumped by the regulator.
Leon
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